This invention is directed to a method of coating a variety of substrates. In particular, this invention is directed to an improved method of curing a composition used as a coating, which method is especially useful for providing a finish for automobiles and trucks.
It is well known that consumers prefer automobiles and trucks with an exterior finish having an attractive aesthetic appearance, including high gloss and excellent DOI (distinctness of image). While ever more aesthetically attractive finishes have been obtained, deterioration of the finish over time, whereby the exterior finish of an automobile or truck loses its luster or other aspects of its aesthetic appearance, may be all the more noticeable. An increasingly observed cause of this deterioration is etching of the finish caused by exposure to environmental chemical attack. Chemicals that may cause etching of a finish include pollutants such as acid rain and chemical smog.
In order to protect and preserve the aesthetic qualities of the finish on a vehicle, it is generally known to provide a clear (unpigmented) topcoat over a colored (pigmented) basecoat, so that the basecoat remains unaffected even on prolonged exposure to the environment or weathering. It is also generally known that alkoxysilane polymers, due to strong silane bonding when cured, exhibit excellent chemical resistance. Exemplary of prior art patents disclosing silane polymers for coating are U.S. Pat. No. 4,368,297; U.S. Pat. No. 4,518,726; U.S. Pat. No. 4,043,953; and Japanese Kokai 57-12058.
However, to applicants' knowledge, none of the previously disclosed alkoxysilane compositions for finishing automobiles or trucks have as yet ever been placed into commercial use. It is believed that heretofore patented or known alkoxysilane coatings may suffer from certain unsolved problems or deficiencies. A significant problem with silane compositions has been the poor shelf life that the compositions exhibit when they contain curing catalysts. As a result, the pot life of a one package system is limited. Further, contamination with water or humidity may even cause premature gelling of the composition, which could render it unusable.
There is a need for a commercially practical finish having excellent appearance, including high gloss and DOI, that is resistant to etching caused by chemical attack. It is desirable that such a finish be readily obtained employing a composition that is not problematic, difficult to apply, unduly subject to premature gelling. It is desirable that such a composition have a good shelf life. It is further desirable that such a composition should be capable of being applied over a variety of basecoats and have excellent intercoat adhesion.